The Vault of Knowledge is a vast storehouse in Orothe, where many magical relics are kept.
Blu is the guardian of the vault.
"Four relic mirrors. Four orpuses. Try and loot the Vault now. I dare ye." -Blu, Vault Guardian
"Me mates and I guard the Vault of Science, and the Vault returns the favor." (Ring of Secrets)
"Tony, I've been guardin' that Vault since I was old enough to hold a trident. Me daddy was a guard afore I was, and his daddy afore him. Nobody ever told any of us about the outside world." (Blu)